Evolution A Human Perspective Human Evolution Human evolution

Evolution A “Human” Perspective

Human Evolution • Human evolution began about 60 million years ago with the earliest primates: mammals with long snouts, sharp teeth and large eyes who lived in trees and fed on insects. • Three distinguishable traits evolved: – Flattened molars to eat plants – Grasping hands with opposable thumbs – Forward directed eyes

Primate Phylogeny • About 30 to 40 million years ago humans evolved into prosimian and anthropoid organisms – Prosimian large eyes, nocturnal, long tail (lemur) – Anthropoid diurnal, feed on fruits and leaves, enlarged brain, social groups and care for young (monkeys, apes and humans)

• About 25 to 30 million years ago the anthropoid lineage split into – Old World monkeys arboreal and ground dwelling, close together nostrils and tails are not prehensile (macaque, baboon) – New World monkeys migrated to South America and evolved in isolation, exclusively arboreal, widely separated flared nostrils and prehensile tails (tamarin, spider monkey, howler monkey) – hominoids most are ground dwelling, longer front limbs than hind limbs and larger brain size relative to body size, no tails (gibbons, orangutans, gorillas, chimpanzees and humans) Primate Phylogeny Olive baboon • Humans share a lot of traits with hominoids – Bipedal motion (wide pelvis & curved vertebral column), enlarged brain, complex language, construction and use of complex tools. Southern Muriqui or wooly spider monkey

Emergence of Humans • Without fossil records Darwin linked apes to humans and that fossil records to prove it would be in Africa. • Hominid (hominin) clade has many branching lineages and related species • Hominin humans and other extinct members of their lineage arising from the most recent common ancestor that humans share with apes. • Australopithecines 6 different species between 4. 2 and 1. 0 million years ago. Generally a group of extinct hominids closely related to humans.

Emergence of Humans • As more fossils are found paleontologists attempt to put together phylogenetic tree for humans. – Homo genus Africa, 2. 4 -1. 6 million years ago • H. habilis H. erectus about 1. 6 million years ago. H. erectus used stone tools and fire. Brain size around 750 cm 3 (1200 cm 3 today), a rounded head and smaller teeth…more like current human features. H. erectus moved out of Africa into Asia and Europe. • H. erectus H. neanderthalensis and H. sapiens about 600 000 years ago. • H. sapiens first appeared in Africa 130 000 years ago and H. neanderthalensis was already living in Europe and Asia

Competing Theories • Multiregional Hypothesis anatomically modern humans evolved in parallel in a number of places (Africa, Europe, Asia). Gene flow accounts for them not becoming distinct species. – Regional genetic diversity arose due to regional selective pressures over about 1 million years. • Monogenesis Hypothesis H. sapiens evolved only in Africa and then migrated displacing Neanderthal and other H. erectus populations. – Regional genetic diversity arose in humans with the past 80 000 to 100 000 years, that is, since H. sapiens left Africa. – Homo sapiens vs. Neanderthals

Did we come from Africa? • If this is true then there should be the greatest amount of genetic diversity there within our genes. The research backs this up. On a highly variable region on chromosome 12 there were 24 different versions discovered: 21 from African populations, 3 in European populations and 2 in Asian and Australian populations. • Similar idea with Y chromosome variability there is more variability in Y chromosomes from Africa.

Did we come from Africa? • It has been found that there is greater genetic diversity among Africans than among Eurasians, and that genetic diversity among Eurasians is largely a subset of that among Africans, supporting the 'out of Africa' mode – African populations have been located in Africa longer with more people so there is more genetic diversity as a result. – Populations that migrated did not have as many people therefore there is less genetic variability in other areas of the world.